Slowly migrating EGF receptor

Hi, I immunoadsorbed the EGF receptor and eluted it, dialyzed to remove the detergent in the presence of added lipid, assayed for tyrosine kinase activity. The sample was heated to 60 C for 3 min. in laemmli's sample buffer and was run on 7.5 % SDS-PAGE. The autoradiogram showed all the active receptors at the very top of the gel. Need help quickly!